Dare I suggest that your article on SAP has the world upside-down (23 July, page 22)?

The science world has only the vaguest quantitative measure of global warming and the contribution to it of carbon dioxide; the possible contribution of the UK to making a change in this is swamped by developing countries elsewhere; and the possible contribution of our new housing is largely swamped by the existing stock. Meanwhile a growing portfolio of social studies demonstrates that calculated savings are swamped by householder behaviour. This is called 鈥渕ultiplying a guess by an estimate鈥�, and out of this comes a series of largely political arbitrary targets.

Perhaps it is good to have targets, but energy conservation is quite different from the structural 好色先生TV Regulations. If a beam is weak, it falls down and someone may be killed. If a roof has the incorrect thermal resistance, then the householder has a slightly larger (or smaller!) bill, but the effect on the world is undetectable. What is certain is any elaboration of the calculation procedure will add a new corps of approved designers, calculators and quality controllers - in other words, increase the overheads on each house. Does 2% sound about right?

So perhaps our objective should be a system that is dead easy to use, and, by and large and on average, delivers the arbitrary political target. Unfortunately, the scientists have got hold of the system-building, and seem to have persuaded you that the objective is accuracy to seven decimal places.

Ian Macpherson

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